1. Field of the Invention
This invention relates to a valve for a vehicle fuel tank, more particularly to an anti-spill valve for installation in the top of the fuel tank of a vehicle, particularly an automobile, for preventing pressure buildup in the tank during normal operation by allowing internal tank pressure to escape to the exterior and for preventing spillage of gasoline to the exterior when the vehicle suddenly accelerates, turns sharply or overturns.
2. Description of the Prior Art
FIG. 20 is a cross-sectional diagram of a prior art valve, and FIG. 21 shows the valve of FIG. 20 turned sideways. In FIGS. 20 and 21, reference numeral 1 denotes a housing formed of synthetic resin, comprising a housing unit 2 and a detachable cap 7. The housing unit 2 has a passage 3a that communicates with the outside, provided in the center of the housing unit 2. Going toward the interior of the housing unit 2, the passage 3a expands into a conical valve seat 3b formed in a round ceiling 3. From the outer edge of the ceiling 3, a cylindrical side wall 4 extends downward. The side wall 4 is provided with a plurality of holes 4a, a plurality of claws 4b around the lower circumference that are thicker toward the upper end, and guide ribs 4c used to guide a float 11 (described below). The guide ribs 4c are of equal height and are disposed axially at set intervals around the inside of the side wall 4. From the center of the ceiling 3, a connecting pipe 5 having a central passage 5a that communicates with the passage 3a extends radially out past the side wall 4. An annular mounting member 6 provided on the outside of the side wall 4 is used to mount the housing unit 2 on a fuel tank.
The cap 7 comprises a cylindrical side wall 8 with radial engaging holes 8a that correspond to the claws 4b on the side wall 4 and float guide ribs 8b disposed axially at set intervals around the inside surface, and a bottom 9 that closes the lower end of the side wall 8. The bottom 9 has a plurality of vertical holes 9a that enable the bottom 9 to function as a filter. Reference numeral 11 denotes a float housed in the housing 1. The float 11 is cylindrical in shape and formed of synthetic resin. The lower end of the float 11 has an annular concave portion 12, and is provided with a plurality of vertical through holes 13 that communicate with the concave portion 12, and a valve head 14 that projects up from the top of the float and operates to open and close the passage 3a by separation from and contact with the valve seat 3b. A coil spring 21 is disposed between the housing bottom 9 and the float 11 to help urge the float 11 upwardly.
Operation of the valve will now be described. The valve is normally mounted on a fuel tank (not shown) with the housing 1 oriented vertically, as shown in FIG. 20. In this state, the float 11 descends under its own weight against the force of the coil spring 21, separating the valve head 14 from the valve seat 3b and opening the passage 3a. Gasoline vapor formed in the fuel tank is therefore able to flow out via the holes 4a and 9a, the space between the side wall 4 and the float 11, and the passages 3a and 5a, preventing the pressure inside the fuel tank becoming elevated.
Although a buoyant force acts on the float 11 when gasoline enters the housing 1 through the holes 9a owing to a large inertial force produced by rapid acceleration or sharp turning of the vehicle, this force alone is not strong enough to raise the float 11 since the specific gravity of the float 11 is greater than that of the gasoline. However, the buoyant force combined with the weak force of the spring 21 acting upwardly on the float is sufficient to raise the float and bring the valve head 14 into close contact with the valve seat 3b, closing the passage 3a and thereby preventing gasoline from flowing out of the fuel tank. When the vehicle returns to a normal state and gasoline in the housing 1 flows back through the holes 9a into the fuel tank, under its own weight the float 11 descends, compressing the spring 21, whereby the valve head 14 separates from the valve seat 3b, opening the passage 3a. If the vehicle should turn over onto its side, the valve will also be turned sideways, as shown in FIG. 21, and the force of the coil spring 21 will move the float 11 in the direction of the passage 3a until the passage 3a is closed by the abutment of the valve head 14 against the valve seat 3b, thus preventing gasoline in the fuel tank spilling to the outside.
In the prior art valve, a clearance h is provided between the guide ribs 4c and the float 11 to allow the float 11 to move smoothly. Therefore, if the vehicle falls on its side, as shown in FIG. 21, the center axis of the valve head 14 (the axis of the float 11) is subjected to a parallel displacement down from the axis of the passage 3a by the amount of the clearance h. In this state, even if the float 11 is moved with the intention of closing the passage 3a with the valve head 14, the valve head 14 will contact the lower sloping face of the conical valve seat 3b. 
In order to have the valve head 14 close the passage 3a, a force is required that lifts the valve head 14. This force is provided by the coil spring 21, but the lifting force is reduced by the high frictional resistance that exists between the sloping portion of the valve seat 3b and the valve head 14. Since this can prevent the passage 3a being promptly and fully closed by the valve head 14, gasoline can leak from the fuel tank.
This invention was accomplished in response to the foregoing circumstances and has as an object to provide a valve that, even when turned sideways, can suppress leakage of fuel to the exterior by promptly closing a passage that communicates with the outside.
For achieving the aforesaid object, the invention provides a valve comprising a housing having an outside-communicating passage and a float provided in the housing that opens and closes the passage by moving axially along the housing, the valve being provided with a float guide means that guides the float to close the passage by means of a gap formed between an inner surface of the housing and an outer surface of the float that increases in size with increasing distance from the passage.
The guide means comprises a float tapered portion provided on the cuter surface of the float that tapers in with increasing distance from the passage, the tapered portion being provided from the outer peripheral edge at the passage end of the float, to where a plane that passes through the center of gravity of the float and is orthogonal to the float axis, intersects the outer surface of the float. The guide means can also be provided on the inner surface of the housing as a housing tapered portion that narrows the housing toward the passage end.
In another aspect of the invention, the float is provided with a pivot support portion at a junction between a float cylindrical surface and a float tapered portion, that is located at a point on the side face of the float intersected by a plane that passes through the center of gravity of the float and is orthogonal to the float axis, and the float tapered portion tapers in away from the passage end. The pivot support portion can be located at a junction between first and second float tapered portions constituting the float tapered portion.
The pivot support portion can be provided as a portion that extends around the whole peripheral surface, or it can be provided as a plurality of sections. When it is provided as a plurality of sections, a plurality of grooves can be used to divide the pivot support portion into a plurality of pivot support portions on the outer surface of the float. Alternatively, the pivot support portion can be divided into a plurality of pivot support portions by providing the outer surface of the float with a plurality of grooves extending parallel to the axis of the float.
As described above, in accordance with the present invention, a configuration is used in which the gap between the inner surface of the housing and the outer surface of the float is larger away from the passage than it is near the passage, which is used to guide the float toward the passage when the valve is turned onto its side. At the point at which the float abuts against the lower part of the angled surface forming the valve seat, or against the ceiling, since the distance between the center axis of the passage and the center axis of the valve head is smaller than in a prior art valve configuration, there is less frictional resistance between the float and the angled surface of the valve seat or the ceiling. Therefore, although the float is urged with the same spring force, the result is that the front of the float is lifted with a larger force than the force used to lift the float in the case of a prior art valve. Thus, the float can quickly close the passage, stopping any leakage of gasoline.
The invention also includes float provided with a pivot support portion about which the float can pivot. In this case, when the valve is turned onto its side, the force of the spring rotates the float as the float is urged forward to stop leakage of gasoline by closing the passage by abutting the valve head against the valve seat.
In accordance with another aspect, a plurality of grooves are provided around the outer surface of the float, with each groove extending axially with respect to the float. When the float reverts to its normal state, this arrangement prevents the float sticking to side walls.
The above and other objects, features and advantages of the present invention will become apparent from the following description made with reference to the accompanying drawings.